1. Field of the Invention
This invention relates to the treatment of diarrhea caused by pathogenic E. coli infection. More specifically, this invention relates to methods for the neutralization of shiga-like toxins (SLT) associated with enteric E. coli infection which methods inhibit progression of this infection into hemolytic uremic syndrome (HUS).
2. References
The following references are cited in the application as numbers in brackets () at the relevant portion of the application.
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M., et al., "Sialic Acid Glycosides, Antigens, Immunoadsorbents, and Methods for Their Preparation", U.S. Pat. No. 5,079,353, issued Jan. 7, 1992. PA0 23. Okamoto, K., et al., "Glycosidation of Sialic Acid," Tetrahedron, 47: 5835-5857 (1990). PA0 24. Abbas, S. A., et al., "Tumor-Associated Oligosaccharides I: Synthesis of Sialyl-Lewis.sup.a Antigenic Determinant", Sialic Acids, Proc. Japan-German Symp. Berlin 22-23 (1988). PA0 25. Paulsen, "Advances in Selective Chemical Syntheses of Complex Oligosaccharides", Angew. Chem. Int. Ed. Eng., 21:155-173 (1982). PA0 26. Schmidt, "New Methods for the Synthesis of Glycosides and Oligosaccharides--Are There Alternatives to the Koenigs-Knorr Method?", Angew. Chem. Int. Ed. Eng., 25:212-235 (1986). PA0 27. Fugedi, P., et al., "Thioglycosides as Glycosylating Agents in Oligosaccharide Synthesis", Glycoconjugate J., 4:97-108 (1987). PA0 28. Kameyama, A., et al., "Total synthesis of stialyl Lewis X", Carbohydrate Res., 209: c1-c4 (1991). PA0 29. 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The disclosure of the above publications, patents and patent application are herein incorporated by reference in their entirety to the same extent as if the language of each individual publication, patent and patent application were specifically and individually included herein.
State of the Art
Diarrhea caused by strains of pathogenic E. coli has been found to be associated with the production of a variety of enterotoxins. Some pathogenic E. coli produce enterotoxins that are closely related to the shiga toxin associated with Shigella-cause dysentery. The first member of the family of shiga-like toxins (SLT) to be isolated was cytotoxic for African Green Monkey (Vero) cells and was originally called verotoxin. Since its structural similarity to shiga toxin has been established by sequencing of the relevant genes, this toxin is now more commonly called shiga-like toxin I (SLTI) [5,6,7].
Additional members of the SLT family have subsequently been isolated that can be distinguished serologically, on the basis of gene sequence, or on host specificity [37-43]. Various types of SLTII have been described and have been assigned various designations depending on the strain of E. coli from which they are isolated and the host affected. Thus variants have been designated SLTII; vtx2ha; SLTIIvh; vtx2hb; SLTIIc; SLTIIvp and so forth.
All of the SLT's are multimeric proteins composed of an enzymatic (A) subunit and multiple (B) subunits. The B oligomer is the binding portion of the toxin that allows it to bind to host cell receptors. The B subunits of SLTI, SLTII and SLTIIvh recognize host cell globoseries glycolipid receptors containing at minimum the disaccharide subunit .alpha.Gal(1-4).beta.Gal at the non-reducing terminus; SLTIIvp has been shown to bind to the receptors containing this subunit but not necessarily to the non-reducing end [2, 44-51]. The A subunit has an enzymatic activity (N-glycosidase) that depurinates 28S ribosomal RNA in mammalian cells. This enzymatic activity abolishes the ability of the toxin-infected cell to perform protein synthesis.
The site for SLT action is endothelial cells found in the kidneys and mesenteric vasculature, and SLTs may cause damage that can result in renal failure and hemoglobin in the urine. SLTs are the causative agent in the hemolytic-uremic syndrome. SLTs may also be partially involved in the pathogenesis of hemorrhagic colitis (bloody diarrhea).
The hemolytic uremic syndrome (HUS) is the leading cause of acute renal failure in childhood and affects approximately 7-10% of children in the 5-10 days following infection with E. coli 0157:H7 and other verotoxin/shiga-like toxin producing E. coli (VTEC).
Recent attention regarding such pathogenic E. coli has focussed on the known correlation between E. coli contamination of certain meats and subsequent infection in humans after ingestion of this meat. The problem is particularly acute with regard to hamburger meat where ingestion of undercooked meat has been found to be the causative factor in the infection. This problem is compounded by the fact that the rapid progression of the pathogenic E. coli infection into HUS via the expression of the SLTs suggests the hypothesis that initial colonization of the intestinal tract is followed by endothelial injury and subsequent kidney involvement via the transmembrane delivery of the SLT toxin into the blood stream of the infected individual.
As a complicating factor, the art suggests against the use of antibiotics in the treatment of enterohemorrhagic E. coli infection [8]. The use of antimotility drugs also appears to be counterproductive [9].
One reported method for the treatment of such infections is to orally administer a pharmaceutically inert affinity support comprising an .alpha.Gal(1.fwdarw.4).beta.Gal subunit to the infected patient [10]. This support passes into the intestinal tract of the patient whereupon the .alpha.Gal(1.fwdarw.4).beta.Gal subunit binds the Shiga-like toxin. Subsequently, the toxin bound to this solid support is eliminated from the body as part of the stool. This procedure is one of the first, if only, reported methods for removing such toxins from the body which, in turn, inhibits manifestation of the conditions associated with toxin accumulation.
Notwithstanding the significant advances made by this reported method, further advances in the treatment of enterohemorrhagic E. coli infections are needed in order to reduce the occurrence of HUS and the high mortality levels associated therewith.